1. Field of the Invention
The present invention relates to a process for the chlorination of polyolefins by a "chlorination-in-bulk method."
In general, the properties of and standards for chlorinated polyolefins may vary depending on the usage of desired products. However, it is required in common use that the chlorinated polyolefins have a residual crystallinity of 0 to 10% and a chlorine concentration of 35.+-.5% to 65.+-.5%.
2. Description of the Prior Art
Hitherto, a number of methods for the chlorination of polyolefins has been proposed. Those methods may be categorized into the three types as set forth below:
(1) An aqueous slurry method in which the chlorination is carried out by using a polyolefin suspension in water. PA1 (2) A solvent method in which the chlorination is carried out by using a polyolefin suspension in an organic solvent. PA1 (3) A fluidized bed method in which the chlorination is performed by fluidizing polyolefins with a mixed gas of nitrogen and chlorine.
The aqueous slurry method includes, for example, U.S. Pat. No. 3,429,865 to J. J. Baron, Jr. et. al., and Japanese Patent Publication No. (Sho)47-13,780. U.S. Pat. No. 3,429,865 discloses a process for the chlorination in which polyolefins are chlorinated in an aqueous slurry in the presence of a non-ionic surfactant. Japanese Patent Publication No. (Sho)47-13,780 teaches a process for the chlorination of polyolefins using a polyolefin slurry of a finely divided, high density polyolefin in an aqueous solution of metal chlorides. U.S. Pat. No. 4,425,206 also discloses a process for the preparation of chlorinated polyethylenes having a relatively low crystallinity which comprises chlorinating a high density polyethylenes in four steps in the presence of a free radical generation accelerant. However, the above mentioned aqueous slurry method suffers from the defects that it is essential to use the reaction chambers which should be lined with expensive anti-corrosive materials, because a low concentration of hydrochloric acid which is useless in view of the industry is formed as a by-product from the methods.
The solvent method have the drawbacks that it need a large amount of energy in the recovery of the solvent used. Nevertheless, the recovery itself of the solvent used is not easily performed; this may result in an amount of the solvent remaining in the final product. The remaining solvent not only deteriorates the quality of the product but also is harmful to the human body.
Finally, the fluidized bed method generally means the method in which the chlorination of polyolefins is carried out in a medium comprising an inert gas such as nitrogen without suspending or dissolving directly polyolefins in a liquid medium such as water or an organic solvent. This method somewhat overcomes the difficulties encountered in either the aqueous slurry method or the solvent method. However, because of using an excess amount of nitrogen gas, the concentration of the hydrogen chloride gas formed as a by-product becomes lowered. Therefore, the hydrogen chloride gas so produced has no use other than the production of hydrochloric acid. Moreover, the processing steps per se involved in this fluidized method are complicated, and the yields thereof are not so good. However, a critical defect is that it is not possible to expect an uniform chlorination for a short period of time due to the coagulation of polyolefins, which happens during the chlorination.